Sickle cell anemia is a heritable disease caused by a mutation in the gene that provides instructions for the production of hemoglobin. Hemoglobin is a protein found in red blood cells that carries oxygen from the lungs to tissues and organs. The sickle cell mutation causes the red blood cells to deform into a sickle shape. These deformed blood cells cannot travel through blood vessels as well as normal cells and are also more likely to form clots.
Eye disease in sickle cell anemia
Eye disease in sickle cell anemia patients can be divided broadly into two conditions: anterior eye disease and posterior eye disease. Anterior eye disease involves the chamber of the eye, while posterior eye disease involves the retina, optic nerve, and the subretinal tissues, the system of blood vessels and cells that provide nutrients to the retina.
Current research indicates that early problems can be seen in the eye prior to vision problems. A dilated eye test can be used to determine whether these issues are present and evaluate if treatments are working to reduce or prevent vision problems.
An early anterior eye abnormality observed in sickle cell anemia is the malformation of the blood vessels in the eye where they become shortened and isolated, possibly because of small blood clots in them. The severity of this symptom correlates with the severity of systemic sickle cell anemia symptoms. Increased eye pressure may also occur and lead to glaucoma, damage to the eye’s optic nerve, which can cause vision loss.
The most significant changes tend to occur in the posterior segment of the eye. These changes can be broadly split into two groups: non-proliferative sickle cell retinopathy (NPSR) and proliferative sickle cell retinopathy (PSR). The frequency of retinopathy (or disease affecting the retina) is greatest in adulthood, affecting up to 42 percent of patients, though it can also occur in children.
Retinal blood vessels can be affected by blood sickling. Just as in other tissues, pressure can build to the point that small blood vessels burst and start bleeding. The lesions produced by these bleeds are visible in dilated eye exams and can affect the health of the retina.
PSR is the most frequent vision-threatening complication in sickle cell anemia, leading to visual impairment in 10-20 percent of patients. In PSR, the blood vessels become blocked, and rather than reforming normally, they divert away from the retina. Without nutrients, the retina starves and can become damaged or die, leading to vision loss.
Eye tests for vision problems
Every eye exam should include measuring intraocular pressure. A numbing drop is applied to the eye, and a small device is gently pressed into the eye for one or two seconds to measure pressure.
The dilated eye exam can be used to find symptoms of anterior eye disease. An atropine-containing eye drop is used to dilate the pupils. This allows the visualization of the blood vessels of the eye and some of the retina. The pupil then relaxes on its own within one to three hours.
Fluorescein angiography is often useful in identifying the areas of the retina that are not being supplied with blood. A fluorescent dye is injected into the blood vessels in the eye and allows their visualization.
Treatment of eye disease in sickle cell anemia
Sickle cell anemia patients have a very poor tolerance to increased pressure in the eye, so aggressive treatment may be necessary. However, some treatments such as carbonic anhydrase inhibitors, hyperosmotic agents, and adrenergic agonists that are used to treat glaucoma can increase cell sickling. Beta blockers and prostaglandin analogs are safer treatment alternatives.
At this time, there are not many preventive treatments for PSR, though there are some surgical interventions available for late-stage symptoms such as retinal detachment.
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